1. Field of the Invention
The present invention relates to improvements in apparatus for transporting racks of specimen-containers to or within an automated clinical instrument for analysis and/or processing. More particularly, this invention relates to a magnetic specimen-transport system that is adapted to transport magnetically-attractable racks of specimen-containers in mutually perpendicular (X/Y) directions across a rack-supporting surface, whereby the racks can be transported among various non-linearly aligned positions on such surface.
2. The Prior Art
It is known in the art to perform diagnostic tests on various liquid biological specimens, e.g., whole blood, serum, urine, spinal fluids, etc., using different automated clinical instruments. In the analysis of whole blood specimens, for example, such automated instruments often include hematology and fluorescence flow cytometry instruments that operate to count and/or differentiate different types of blood cells on the basis of their respective physical, optical and/or electrical properties. The specimens to be analyzed by such instruments are commonly collected in various types of test tubes or containers. Each container is normally sealed at its top by a puncturable rubber cap through which a movably-mounted aspiration probe of each instrument can enter and withdraw a desired aliquot of specimen for processing. Typically, five or six specimen-containers, each bearing encoded patient and test information in the form of a bar code or the like, are supported for aspiration by a single rack or cassette. The rack serves to align and equally space the containers to simplify the required movement of the instrument's aspiration probe in order to gain access to the interior of each container. In some instruments, the aspiration probe is located within the interior of the instrument housing; in such instruments, an integral specimen-transport system within the instrument is used to present the specimen-container racks to the probe for aspiration. In other instruments, the aspiration probe is movably-mounted on the exterior of the instrument housing; with such instruments, an external specimen-transport device or module is used to present specimen-containers to a location that accommodates the allowed movement of the aspiration probe outside the instrument housing.
U.S. Pat. No. 5,720,377, filed in the names of Lapeus et al., discloses a specimen-transport module of the type noted above. The module operates to present individual racks of specimen-containers to an externally-accessible aspiration probe of an associated clinical instrument. The module generally comprises three interrelated trays, viz., (a) an elongated input tray that is adapted to receive and temporarily store a linear queue of specimen-container racks, (b) a movably-mounted process tray that is adapted to receive racks of specimen-containers, one at a time, from the input tray and to present them to a location for specimen-aspiration and testing, and (c) an elongated output tray that is adapted to receive processed racks one at a time from the process tray and to temporarily store such racks in a linear output queue for subsequent retrieval. The input and output trays are linearly aligned, end-to-end, and each tray is provided with linear guides that interact with features on the racks to align the received racks to form the respective linear queues. The process tray is positioned adjacent to the input and output trays and extends parallel to these trays. Each of the racks comprising the input queue is forwardly advanced over the rack-supporting surface of the input tray by a magnetic transport system that underlies the input tray. The input tray is made of a nonmagnetic material (in this case, aluminum), and each specimen-container rack carries one or more magnetically-attractive members in its base portion. The magnetic transport system that underlies the tray comprises a pair of parallel conveyor belts, each carrying a plurality of permanent magnets at equally spaced locations. The belts are trained about spaced pulleys, and one reach of each of the belts is closely spaced from the underside of the input tray and extends in a direction parallel to the linear guides. As the belts are driven along their respective endless paths, the respective magnetic field of one or more of the permanent magnets carried by the belts passes through the input tray and magnetically couples with the magnetically-attractive member(s) of one or more of the racks. Thus, as the belt moves under the input tray, the magnetically coupled racks atop the tray are pulled along the linear path defined by the guides to a location where the foremost rack in the queue can be acted upon by a second conveyance of the transport system. The latter operates independently of the magnetic drive system to physically engage and push each rack from the input queue into an awaiting slot of the movably-mounted process tray. Upon presenting a rack of containers to the associated clinical instrument for processing, the process tray slides forward to a location where the processed rack can be acted upon by a third conveyance which operates to physically push the rack out of the process tray and onto the output tray, where the processed racks are guided to form the linear output queue. A fourth conveyance then operates to physically push the output queue of racks over the output tray surface to an off-lading position.
As noted in the above patent, the use of magnetic forces to advance specimen-container racks within a specimen-transport module affords certain advantages over the mechanical schemes that are commonly used to physically engage and push or pull a rack along a desired path. Since the drive mechanism for magnetically advancing racks is located below the input tray and within the housing of the transport system, its moving parts are totally isolated from the user environment and, hence, pose no potential safety hazards to the user. Moreover, since the surface of the input tray over which the specimen-container racks is moved by the magnetic transport system is plane and featureless, liquid spills, dust and dirt can be removed with relative ease. While the magnetic transport system disclosed in the above patent affords these advantages, the disclosed system can operate only to advance specimen-container racks along a linear path, e.g., that found in the transport module's input buffer; thus, its utility is substantially limited. Further, since the permanent magnets are supported by flexible endless belts, each being supported only by a pair of spaced pulleys, any tendency for the belts to sag between the pulleys will change the displacement between the magnets and the magnetically-attractive members of the racks, thereby causing an undesirable variation in the attractive force between these elements.